Date: Tue, 31 Oct 2017 23:58:52 -0700
From: Kurt Andress <andresskurt@gmail.com>
To: towertalk@contesting.com, jim.thom@telus.net
Subject: [TowerTalk] Wind survival + load ratings... vs, reality.
Hi Jim,you wrote...
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Thomson
Sent: Tuesday, October 31, 2017 1:53 PM
To:towertalk@contesting.com
Subject: [TowerTalk] Wind survival + load ratings... vs reality.
Has anybody tried stuffing yagi manufactures ele dimensions into software
like Yagi stress..... and or Yagi max ????
I have been doing just that on a bunch of them...and in several cases, Im not
impressed with the results.
And Im using the correct dimensions for exposed length tubing, and correct OD
and wall thickness, and correct
yield strength. Im using both the ... no spec..aka wind tunnel
spec.......and also the old C spec.
Some of these yagis that are rated at ... 100 mph are actually only good for a
paltry 64 mph...and that?s with NO ice,
such is the case with the M2 80m yagis. Their 3 el 80m yagi uses C specs
for wind area. They rate it at 32 sq ft.
Its actually 48 square foot of projected area. Their combo truss + LL does
nothing for ice loading, and nothing for
horizontal deflection. The LL reduces some ele sag, thats it. Both YS +
YM spit out 64 mph using no spec..and
both spit out 69 mph, using C spec...and that?s with NO ice.
Toss just .25 inch of ice into the mix, and it becomes 48 mph using no
spec....and 52 mph using C spec.
The optibeam 80m yagi doesnt fare much better. Good for 72 mph, using C
spec....and less using no spec....and that?s with NO ice.
I also tried the JK antennas 3 el 80m yagi in YM + YS. Using no spec, it
comes in at 103 mph. Using C spec, its good for 107 mph.
Now that?s a helluva big difference between m2s 64 mph...and the JK?s 103
mph. Considering the M2 is not cheap at $9935.95
I have also stuffed several other yagis, like 40m, and 20, and multibanders
etc through the software. Eye opener, but not as bad as
the 80m yagis above. I tried Mosley, Hy-gain, old telrexs, KLM, and anything
else I could get exact dimensions for.
Back in the day, ant makers could get away quoting BS gain and FB
numbers...... until software came along. They are still doing it,
but with BS wind load ratings, and max wind survival ratings. The
mechanical software is readily available, so why isnt anybody holding them
accountable ?
In a lot of cases, hams are being sold a... bill of goods.
Jim VE7RF
<W3JK, who uses my software, put me onto this post...
<Now you guys are catching up with me, from the work I did in the 1980's to spend
about 8 years creating YagiStress, and getting it verified by one of my P.E.
colleagues with $18k software, Yagistress is within ~ 1% (or rounding errors) with
the pro finite <element linear analyzing engines.
<What you're seeing Jim is what I have seen for around 30 years, and I have made comments on
this reflector many times about that, but they were greatly ignored! I got run off this
platform by too many other jungle knowledge experts that want to rule the <roost with their
ever present emperical expertise! So, that's why I no longer devote much of my time to this
venue....it is frought with way more "Jungle Knowledge" than engineering expertise!
<Have fun out there imagining how you wish it would be, but not how it is!
<73, Kurt Andress, K7NV, author of the YagiStress software...and tower service
provider
<P.S. You should simply throw away the EIA/TIA 222-C spec, it is now about 28
years old and does no longer apply!
## Points well taken. What I still dont get is.... the effects of the element
tips bending. I call that...shedding wind. I dont believe the software
factors that effect into the equation. I have seen F12 els, where the tips
and inboard sections from the tips, are bent straight back, and the even more
inboard sections still dont break ! IE: when the ends bend way back, the wind
is now hitting them at a shallow angle..and less force applied to the ele ends.
The cross flow principle, so to speak. Having said all that, when m2 is good
for 64 mph..and the JK is good for 103 mph, thats a HUGE disparity..... yet
both are rated for...100 mph. In actuality, the actual breaking mph is
probably 20 % higher than what the software spits out.
## M2, F12, Mosely, Hygain, STILL use the outdated 222-C spec. You have to add
exactly 50% to their square footage, to get the real projected areas. To find out
what their yagis are really rated at, you have to take their eles, typ the REF..and
stuff the dimensions into either YS or YM.... then judge for yourself. I dont
mess with the C spec, nor the 222-F spec, nor the UBC-97 – exposure B/C/D
spec. I use the... No spec, aka wind tunnel...and so do many others.
Heres what YM spits out for the m2 80m REF using various standards.
No wind spec - 64.802 mph
EIA-222-C spec - 69.759 mph
EIA-222-F spec @ 100 ft - 50.397 mph
UBC- 97 Exposure B @ 100 ft - 60.492 mph
UBC- 97 Exposure C @ 100 ft - 50.093 mph
UBC- 97 Exposure D @ 100 ft - 45.549 mph
Use a 200’ tower instead of a 100 ft tower....and they all drop aprx 5 mph.
IMO, measure the speed at the top of your mast... using a wireless, accurate,
peak reading, wind speed indicator. Forget the fastest mile..and 3 sec gust
bs. I want the actual peak wind speed, and if a gust comes along, its the
gust speed that I use. Its also the gusts that break stuff. The sustained
wind speed is nice to know.... but its the higher speed gusts that I want to
know about. I dont want a wind speed indicator on the side of a tower either,
nor the side of a mast. Depending upon wind direction, the tower ..or mast
could impede airflow, and result in a lower reading. Taking the wind speed
from the 6 oclock news is a wasted effort. Done on the far side of town, at a
much lower elevation, typ 33 feet.
I would suggest to JK ants, who actually builds the...real deal, to tabulate
both his ants, and all his competitors using YS + YM....then post the results
on his website... for all prospective clients to see for themselves. Then if
the competitors whine + complain... too bad so sad, either put up...or shut up.
Since his competitors use the C spec, I would suggest posting both the C
spec..and also the NO spec...aka wind tunnel results. Then at least joe ham
can compare yagis...using the same spec. M2 Stating their 80m yagi is 32 sq
ft and good for 100 mph, when software sez its 48 sq ft and good for 64 mph is
nothing short of reprehensible. Then folks can use the correct info to make
an informed decision as to actual tower type required, and also rotational
torque required....and if a given yagi meets their site dependent WX
requirements for expected max windspeed and gusts..and any ice loading, or
heavy wet snow. While we are on a rant, lets minimize ant torque. Easily
done with either a small counterweight and or a Torque compensation plate.
If one of these large 200-500 lb yagis ever cut loose... and came crashing
down....and sliced a phillystran guy wire, or a solid fiberglass guy wire.....
the entire tower could easily come down. Neither philly nor solid fiberglass
has any shear strength.... only good tensile strength. Thats a safety issue
imo.
Id be right pissed if my competitors were spewing BS numbers. And no, a cross
bar mounted above either an element or boom, with dual truss lines on either
side, doesnt increase the max wind speed. Heck it doesnt even reduce the
horz deflection.
end of rant.
Jim VE7RF
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